Saudi-led aircraft pounded Iran-allied Houthi militiamen and rebel army units in central Yemen and the capital Sana'a on Monday despite a formal end to the airstrikes, residents said, and a humanitarian crisis worsened as both sides blocked aid.

Residents said warplanes flew between 15 and 20 sorties against groups of Houthi fighters and arms depots in the al-Dhalea provincial capital, Dhalea, and the nearby city of Qa'ataba, between dawn and 9 a.m. local time (0600 GMT), setting off a chain of explosions that lasted for two more hours.

Fighting intensified on Sunday, after a lull following an announcement by Riyadh last week that it was ending its nearly five-week-old bombing campaign except in places where the Houthis were advancing.

A coalition of Arab countries led by Saudi Arabia, rattled by what they saw as expanding Iranian influence in the Arabian Peninsula, is trying to stop Houthi fighters and loyalists of former President Ali Abdullah Salah taking control of Yemen.

Food deliveries

Vital aid was reported to be being held up by both sides. Houthis were stopping convoys of trucks reaching Aden and an arms blockade by Saudi-led coalition navies searching ships for weapons was holding up food deliveries by sea.

Telecommunications within Yemen and with the outside world could be cut within days due to a shortage of fuel, state-run news agency Saba quoted the director of telecommunications as saying. Fuel shortages were also preventing traders from moving food to market, the United Nations' World Food Program said.

Saudi-led warplanes also struck the area around the presidential compound in Sana'a for a second day, while heavy street fighting was under way in the strategically important city of Taiz in central Yemen, according to residents and the International Committee of the Red Cross.

There were no immediate reports on the extent of casualties.

Fighting has killed more than 1,000 people, including an estimated 551 civilians since the bombings started on March 26, the United Nations said on Friday. Its children's agency UNICEF said at least 115 children were among the dead.

Saudi Arabia, the world's top oil exporter and arch Sunni Muslim regional rival of Shi'ite Muslim Iran, says it was concerned for its own security and Yemen's stability after Houthi forces began advancing across the country, on its southern border, in September, when the Shi'ite militia captured the capital.

The airstrikes have increased the regional tension, with the commander of Iran's elite Revolutionary Guards, General Mohammad Ali Jafari, comparing Saudi Arabia to Tehran's arch-enemy, Israel. “Saudi Arabia is following in the Zionist regime's footsteps in the Islamic world,” Jafari was quoted as saying by the official IRNA news agency.

The Houthis allege President Abd-Rabbu Mansour Hadi fostered Islamist militants linked to al-Qaida and corrupt officials. Hadi, who fought al-Qaida when he had control of the country, says the Islamist militant group is as much a threat to Yemen as it had always been.

The Houthi advance eventually forced Hadi into exile into Saudi Arabia, and Riyadh says it wants to restore Hadi and prevent Yemen disintegrating as a state, with al-Qaida militants thriving in the chaos and one of the world's busiest oil shipping lanes off the Yemeni coast at risk.

The fighting, which pits the Houthis against Sunni tribesmen and Islamist militants, with army units on both sides, has made life increasingly perilous for the country's 25 million people, who rely on imports for more than 90 percent of their food.

Residents of the southern port city of Aden said bread was in short supply and a convoy of trucks carrying flour from the Red Sea port city of Hodeida was being prevented by the Houthis from entering the city.

Convoys blocked

The Houthis also blocked a convoy of ICRC trucks carrying medical supplies to Aden, but contacts were underway to allow the supplies in.

“Our convoys were blocked from going to Aden and Marib over the weekend and we are in discussions with the Houthis to resolve that,” ICRC spokeswoman Sitara Jabeen told Reuters.

Meanwhile, the U.N.'s World Food Program said it was using its stocks inside Yemen to meet humanitarian needs.

“We're noticing price rises and hoarding, with fuel shortages having an impact on the ability of traders to move food to markets, if any of them are actually open to begin with,” a WFP spokesman said.

“Residents of Aden and Sana'a are reporting shortages of wheat flour.”